Biomass gasification is the thermo-chemical conversion of biomass into a combustible gas mixture (producer gas) through a partial combustion route with air supply restricted to less than that theoretically required for full combustion.
Biomass gasification involves burning of biomass in a limited supply of air to give a combustible gas consisting of carbon monoxide, carbon dioxide, hydrogen, methane, water, nitrogen, along with contaminants like small char particles, ash, and tars.
During devolatization, methane and other hydrocarbons are produced from the biomass by the action of heat which leaves a reactive char.
During combustion, the volatiles and char are partially burned in air or oxygen to generate heat and carbon dioxide.
In the reduction phase, carbon dioxide absorbs heat and reacts with the remaining char to produce carbon monoxide (producer gas).
The presence of water vapor in a gasifier results in the production of hydrogen as a secondary fuel component.
There are two main types of gasifier that can be used to carry out this conversion, fixed bed gasifiers, and fluidized bed gasifiers.
The conversion of biomass into a combustible gas involves a two-stage process.
The first, which is called pyrolysis, takes place below 600°C when volatile components contained within the biomass are released.
In addition, there are a number of methods that can be used to produce higher quality product gases, including indirect heating, oxygen blowing, and pressurization.
After appropriate treatment, the resulting gases can be burned directly for cooking or heat supply, or used in secondary conversion devices, such as internal combustion engines or gas turbines, for producing electricity or shaft power (where it also has the potential for CHP applications).
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